When an oil well is drilled, the drill bit is positioned at the bottom of the drill string, and a set of heavy thick walled drill collars is located in the drill string immediately above the drill bit. The drill collars add stiffness to the drill string, control the weight on the drill bit, and thereby control lateral drift of the bit which thus controls the deviation of the hole being drilled. The number of drill collars in a drill string will vary depending upon the depth of the well, the particular formations encountered, etc.
During the drilling of an oil well which is typically considered deep well drilling, there is ample opportunity for the drill string to be seized at the drill collars. Typically, this will happen when a portion of the side wall of the well bore collapses and portions of the formation falls into the annulus between the pipe and the wall of the well bore, thereby causing seizing of the drill string at the drill collars. Even if the hole partially collapses well above the bottom of the hole, the formation material which falls into the annulus will accumulate just above the drill bit and thereby cause seizing of the drill string near the drill collars. Alternately, the presence of formation material between the drill pipe and the formation will cause the drill bit to be deflected somewhat and will thus cause the drill bit to drift from its intended course by virtue of the transverse force applied to it by the collapsed formation material. This places the drill string in a transverse bind so that it wears away the side of the well bore and forms a key seat where the drill collars are forced to the side of a part of the hole which was previously drilled. Such key seating forms narrow sections of the formation which are encountered as the collars are moved upwardly, thereby preventing extraction of the drill string from the well bore.
When, for any of the above mentioned reasons, or for other reasons not named, the drill string is seized, it is necessary to free it up. There are several ways of doing this. One way is to employ a well jar in the drill string for purposes of imparting a substantial impact to the drill string in the immediate vicinity of the place where it is stuck. Since sticking of the drill pipe typically occurs just above the drill bit at the drill collars, a jar mechanism in the drill string is quite advantageous.
Various pipe jarring devices have been provided heretofore which are particularly adapted to be utilized in drill strings and for otherwise releasing stuck well pipe. In most cases, well jars employ a pair of inner and outer telescoping members permitting relative movement of an upper section of pipe or a wire line tool, etc., relative to a stuck lower section of pipe. When the telescoping members are pulled to the full extent thereof, jarring occurs, which, after a time will loosen the well pipe and allow it to be removed from the well. Jarring activity can occur on upward movement, downward movement or both.
Obviously, in the case of deep wells, it is difficult, if not impossible, to impart rapid jarring movement to stuck well pipe since the apparatus being moved within the well due to its significant weight is not capable of rapid movement by way of the surface equipment. In such case, it is desirable that the well jar have an inherent internal jarring activity by virtue of its construction. The present invention provides such an inherent jarring activity even during relatively slow upward or downward movement of the jar controlling system. It is believed, therefore, that the present invention provides a unique system for imparting efficient jarring activity to stuck well pipe and thus the invention constitutes a significant advance over prior well jar mechanisms.
A typical well jar employs a hydraulically operable detent to restrain upward movement of a mandrel within a housing while a strain is taken in the pipe string to stretch it and thereby store a large amount of potential energy. The detent meters slowly to a released position where the mandrel is allowed to move freely upward. Contraction of the pipe string accelerates the mandrel upward to bring a hammer surface thereon against an anvil surface on the housing in a violent manner. The jar is recocked by lowering the pipe string and mandrel to reengage the hydraulic detent, so that a series of jarring blows can be delivered to the stuck object. This type of well jar is shown and described, for example, in U.S. Pat. No. 2,645,459 issued July 14, 1953 to Wayne Sutliff. FIG. 5 of the patent suggests that the same concepts can be used in a wireline jar, with potential energy being stored by stretching the wireline 67.
The Sutliff-type jar is not designed to deliver a downward jarring blow. Even if the assembly were to be run upside down so that a downward blow is possible, only the weight of the pipe string is available to cause the hydraulic detent to meter to its released position and to bring the hammer against the anvil. If the well is deviated to any significant degree, the tubing will lay against the casing walls to produce frictional forces that reduce the weight available to operate the jar. This factor will extend the delay time for the hydraulic detent to meter free, and may prevent operation of the jar at all. Of course a wireline suspended jar would not work because there is no weight available to even operate the detent, or to cause an impact blow to be struck.
Thus the typical wireline jar has for many years taken the form of telescoping upper and lower links. The upper link can be raised quickly by the wireline to cause it to impact against the lower link and deliver an upward blow, or can be dropped against the lower link to deliver a downward blow. In well bores that are substantially vertical, the link-type wireline jar works well to shear pins and other devices as required. However, in deviated well bores, at least the upper link will tend to lay against the wall of the pipe, and here again frictional forces come into play that reduce operational efficiency, and may even prevent operation altogether.